This application claims priority to Japanese Patent Application No. 243379/2000, filed on Aug. 10, 2000 in Japan, and Japanese Patent Application No. 243381/2000, filed on Aug. 10, 2000 in Japan. The contents of the aforementioned applications are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a control system and method and an engine control unit for an internal combustion engine, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
2. Description of the Prior Art
Conventionally, as a control system for an internal combustion engine of a port injection type, an ignition timing control system, for instance, is known which has been proposed by Japanese Patent Publication (Kokoku) No. 7-59925. In this control system, the ignition timing is determined based on the amount of intake air and the rotational speed of the engine, and at the same time, the ignition timing is more retarded as the engine temperature is higher. The retardation of the ignition timing is carried out for prevention of knocking which tends to more readily occur as the combustion temperature rises with a rise in the engine temperature. Further, in the internal combustion engine of a port injection type, fuel is injected toward an intake port during the intake stroke, and an air-fuel mixture is subjected to homogeneous combustion in a state evenly distributed throughout the combustion chamber.
Further, an internal combustion engine of an in-cylinder injection type is also known which in which the combustion mode of the engine is switched between a homogeneous combustion mode in which fuel is injected during the intake stroke and a stratified combustion mode in which fuel is injected during the compression stroke. In general, in this type of internal combustion engine, in the homogeneous combustion mode, fuel is injected into the cylinder during the intake stroke, similarly to the above port injection-type engine, while in the stratified combustion mode, fuel is injected toward a piston during the compression stroke, and evaporated through thermal exchange with the piston to form an air-fuel mixture, and the mixture is subjected to stratified combustion in the state of the mixture being unevenly distributed or concentrated in the vicinity of the spark plug.
When the retardation of ignition timing by the conventional ignition timing control system described above is applied to the above in-cylinder injection-type engine, in the homogeneous combustion mode, knocking is prevented by the retardation of ignition timing based on the engine temperature since the mixture is subjected to homogeneous combustion similarly to the port injection-type engine. On the other hand, in the stratified combustion mode, since the mixture is subjected to stratified combustion, the ignitionability and conditions of occurrence of knocking ascribable to a rise in the engine temperature are different from those in the homogeneous combustion mode. Therefore, if the same retardation of ignition timing is carried out as in the homogeneous combustion mode, combustion efficiency can be degraded due to delay of ignition caused by the retardation of ignition timing which is carried out even though knocking does not occur. This leads to degraded drivability due to decreased engine output and poor fuel economy.
Further, as the aforementioned control system for an internal combustion engine of an in-cylinder fuel injection type, a control system for controlling the fuel injection timing and the amount of fuel to be injected is disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 10-47111. In this control system, the volumetric efficiency is determined based on the intake air amount, and engine load (target average effective pressure) is determined based on accelerator opening and engine rotational speed. Further, the combustion mode is switched between the stratified combustion and the homogeneous combustion mode, is dependence on the engine rotational speed and engine load. Further, combustion parameters, such as a target air fuel ratio, fuel injection timing, ignition timing, and a target EGR rate, are determined by searching respective maps based on the engine rotational speed and engine load when the engine is in the stratified combustion mode, and based on the engine rotational speed and volumetric efficiency when the engine is in the homogeneous combustion mode.
Generally, in the in-cylinder injection-type engine, to enhance the fuel economy and reduce exhaust emissions, when the engine is in the stratified combustion mode, the EGR rate is controlled to a larger value and the intake pipe pressure is controlled to a higher value close to atmospheric pressure than when the engine is in the homogeneous combustion mode. That is, the valve opening of the EGR valve and the valve opening of the throttle valve are controlled to respective larger values. This can cause the target value of the EGR rate and that of the intake air amount to be largely changed, and in such a case, due to a large change in the intake air amount, the intake air can be unstable. In contrast, in the conventional control system described above, in the homogeneous combustion mode, the combustion parameters are calculated based on the volumetric efficiency determined based on the intake air amount, and therefore if the intake air becomes unstable upon transition to the homogeneous combustion mode, the combustion parameters cannot be calculated properly. This can lead to degraded fuel economy, increased exhaust emissions, and degraded drivability.
Further, in the stratified combustion mode, fuel is more difficult to ignite than in the homogeneous combustion mode, and the combustion is more likely to be unstable. Therefore, in the stratified combustion mode, to ensure stable combustion, the ignition timing is required to be set in a more optimized manner than in the homogeneous combustion mode. The conventional control system, however, in the stratified combustion mode, ignition timing is calculated only based on the accelerator opening and engine rotational speed, and hence it is impossible to set the ignition timing to an appropriate value in which the state of combustion and operating conditions of the engine are properly reflected.
It is a first object of the invention to provide a control system and method and an engine control unit for an internal combustion engine, which are capable of properly determining ignition timing in both of a homogeneous combustion mode and a stratified combustion mode to attain a high combustion efficiency, thereby improving drivability and fuel economy.
It is a second object of the invention to provide a control system and method and an engine control unit for an internal combustion engine, which are capable of properly determining combustion parameters including ignition timing, based on operating conditions and a state of combustion of the engine, such that stable combustion is ensured, thereby attaining improved fuel economy, excellent drivability, and reduced exhaust emissions.
To attain the first object, according to a first aspect of the invention, there is provided a control system for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, wherein the control system controls ignition timing of the engine.
The control system according to the first aspect of the invention is characterized by comprising:
an engine temperature-detecting module for detecting an engine temperature of the engine;
a combustion mode-determining module for determining which of the homogeneous combustion mode and the stratified combustion mode should be selected as the combustion mode; and
an ignition timing-setting module for setting a first ignition timing for the homogenous combustion mode and a second ignition timing for the stratified combustion mode to respective values different from each other, and at the same time setting the first ignition timing for the homogeneous combustion mode such that the first ignition timing for the homogeneous combustion mode is more retarded as the detected engine temperature is higher.
According to this control system, the combustion mode-determining module determines which of the homogeneous combustion mode and the stratified combustion mode should be selected as the combustion mode, and the ignition timing-setting module sets a first ignition timing for the homogenous combustion mode and a second ignition timing for the stratified combustion mode to respective values different from each other, and at the same time sets the first ignition timing for the homogeneous combustion mode such that the first ignition timing for the homogeneous combustion mode is more retarded as the detected engine temperature is higher. This enables the control system according to the first aspect of the invention to prevent occurrence of knocking as properly as in the prior art. Further, as described hereinbefore, the state of combustion of an air-fuel mixture is different between the stratified combustion mode and the homogeneous combustion mode, and hence ignitionability and conditions of occurrence of knocking are different between the two modes. Therefore, by setting the first ignition timing for the homogeneous mode and the second ignition timing for the stratified combustion mode to respective different values such that the above-mentioned difference in the ignitionability and conditions of occurrence of knocking value between the homogeneous combustion mode and the stratified combustion mode are reflected in the different values, it is possible to achieve high combustion efficiency even in the stratified combustion mode as well. As a result, it is possible to improve drivability and fuel economy both in the homogeneous combustion mode and the stratified combustion mode.
To attain the first object, according to a second aspect of the invention, there is provided a control method for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke, wherein the control method controls ignition timing of the engine.
The control method according to the second aspect of the invention is characterized by comprising the steps of:
detecting an engine temperature of the engine;
determining which of the homogeneous combustion mode and the stratified combustion mode should be selected as the combustion mode; and
setting a first ignition timing for the homogenous combustion mode and a second ignition timing for the stratified combustion mode to respective values different from each other, and at the same time setting the first ignition timing for the homogeneous combustion mode such that the first ignition timing for the homogeneous combustion mode is more retarded as the detected engine temperature is higher.
This control method provides the same advantageous effects as described above concerning the control system according to the first aspect of the invention.
To attain the first object, according to a third aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out control of ignition timing of an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
The engine control unit according to the third aspect of the invention is characterized in that the control program causes the computer to detect an engine temperature of the engine; determine which of the homogeneous combustion mode and the stratified combustion mode should be selected as the combustion mode; and set a first ignition timing for the homogenous combustion mode and a second ignition timing for the stratified combustion mode to respective values different from each other, and at the same time set the first ignition timing for the homogeneous combustion mode such that the first ignition timing for the homogeneous combustion mode is more retarded as the detected engine temperature is higher.
This engine control unit provides the same advantageous effects as described above concerning the control system according to the first aspect of the invention.
Preferably, the ignition timing-setting module sets the second ignition timing for the stratified combustion mode to a more advanced value than a value of the first ignition timing for the homogeneous combustion mode, with respect to an identical value of the detected engine temperature.
In general, in the case of the internal combustion engine of an in-cylinder ignition type, an air-fuel mixture is ignited in a state concentrated in the vicinity of a spark plug, and at the time of combustion, the mixture is surrounded by air, so that even if the ignition timing is advanced, knocking hardly occurs, and hence no problem is caused. Further, in the stratified combustion mode, fuel is evaporated due to thermal exchange with the piston to produce an air-fuel mixture, and therefore as the engine temperature is higher, the production of the mixture is accelerated. Therefore, by advancing the ignition timing as the engine temperature is higher, delay of ignition can be prevented to enhance the combustion efficiency of the engine. Therefore, in the control system according to the preferred embodiment, by setting the second ignition timing for the stratified combustion mode to a more advanced value than the value of the first ignition timing for the homogeneous combustion mode with respect to an identical value of the engine temperature, higher combustion efficiency and larger engine output can be obtained. As a result, the drivability and fuel economy can be positively improved.
Preferably, the step of setting the first ignition timing and the second ignition timing includes setting the second ignition timing for the stratified combustion mode to a more advanced value than a value of the first ignition timing for the homogeneous combustion mode, with respect to an identical value of the detected engine temperature.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, when the control program causes the computer to set the first ignition timing and the second ignition timing, the control program causes the computer to set the second ignition timing for the stratified combustion mode to a more advanced value than a value of the first ignition timing for the homogeneous combustion mode, with respect to an identical value of the detected engine temperature.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the engine includes a fuel injection valve for injecting the fuel into the cylinder, the cylinder having a top wall facing a combustion chamber, and the fuel injection valve is arranged in a central portion of the top wall such that the fuel injection valve injects the fuel downward therefrom.
According to this preferred embodiment, the advantageous effects provided by the control system and method and the engine control unit according to the first to third aspects of the invention and their preferred embodiments described above can be obtained in an optimized manner.
To attain the second object, according to a fourth aspect of the invention, there is provided a control system for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
The control system according to the fourth aspect of the invention is characterized by comprising:
a load-detecting module for detecting a load on the engine;
a combustion parameter-determining module for determining a first combustion parameter for the homogeneous combustion mode other than a first ignition timing for the homogenous combustion mode and a second combustion parameter for the stratified combustion mode other than a second ignition timing for the stratified combustion mode, based on the detected load;
a first ignition timing-determining module for determining the first ignition timing for the homogenous combustion mode based on the detected load; and
a second ignition timing-determining module for determining the second ignition timing for the stratified combustion mode based on the second combustion parameter.
According to this control system, the first combustion parameter for the homogeneous combustion mode other than the first ignition timing for the homogenous combustion mode and the second combustion parameter for the stratified combustion mode other than the second ignition timing for the stratified combustion mode are determined based on the load on the engine. This makes it possible to determine the first combustion parameter and the first ignition timing properly for the homogeneous combustion mode without being adversely affected by instability of intake air which can occur upon termination of transition from the stratified combustion mode to the homogeneous combustion mode, differently from the prior art in which the first combustion parameter for the homogeneous combustion mode is determined based on the amount of intake air. Further, according to this control system, the second ignition timing for the stratified combustion mode is determined based on the second combustion parameter other than the second ignition timing determined based on the load on the engine. This makes it possible to properly determine the second ignition timing by reflecting operating conditions and state of combustion of the engine thereon. As described above, by properly determining the combustion parameters including the first and second ignition timings, it is possible to ensure stable combustion in both of the homogeneous combustion mode and the stratified combustion mode.
To attain the second object, according to a fifth aspect of the invention, there is provided a control method for an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
The control method according to the fifth aspect of the invention is characterized by comprising the steps of:
detecting a load on the engine;
determining a first combustion parameter for the homogeneous combustion mode other than a first ignition timing for the homogenous combustion mode and a second combustion parameter for the stratified combustion mode other than a second ignition timing for the stratified combustion mode, based on the detected load;
determining the first ignition timing for the homogenous combustion mode based on the detected load; and
determining the second ignition timing for the stratified combustion mode based on the second combustion parameter.
This control method provides the same advantageous effects as described above concerning the control system according to the fourth aspect of the invention.
To attain the second object, according to a sixth aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out control of an internal combustion engine of an in-cylinder fuel injection type, the engine being operated while switching a combustion mode thereof between a homogeneous combustion mode in which fuel injection into each cylinder is performed during an intake stroke, and a stratified combustion mode in which the fuel injection into the cylinder is performed during a compression stroke.
The engine control unit according to the sixth aspect of the invention is characterized in that the control program causes the computer to detect a load on the engine, determine a first combustion parameter for the homogeneous combustion mode other than a first ignition timing for the homogenous combustion mode and a second combustion parameter for the stratified combustion mode other than a second ignition timing for the stratified combustion mode, based on the detected load, determine the first ignition timing for the homogenous combustion mode based on the detected load, and determine the second ignition timing for the stratified combustion mode based on the second combustion parameter.
This engine control unit provides the same advantageous effects as described above concerning the control system according to the fourth aspect of the invention.
Preferably, the second combustion parameter is a fuel injection timing, and the combustion parameter-determining module comprises a final fuel injection amount-determining module for determining a final amount of fuel to be injected into the cylinder in the stratified combustion mode, based on the detected load, and a fuel injection timing-determining module for determining the fuel injection timing based on the determined final amount of fuel to be injected into the cylinder.
According to this preferred embodiment of the control system, in the stratified combustion mode, the final amount of fuel to be actually injected into the cylinder in the stratified combustion mode is determined based on the load on the engine, and the fuel injection timing for fuel to be actually injected is determined based on the final amount of fuel. Further, the second ignition timing for the stratified combustion mode is determined based on the fuel injection timing. Therefore, the second ignition timing for the stratified combustion mode can be determined in a manner suited to the final amount of fuel to be actually injected and the fuel injection timing for fuel injection to be actually carried out. This further positively ensures a stable combustion of the engine.
Preferably, the second combustion parameter is a fuel injection timing, and the step of determining the first combustion parameter and the second combustion parameter comprises the steps of determining a final amount of fuel to be injected into the cylinder in the stratified combustion mode, based on the detected load, and determining the fuel injection timing based on the determined final amount of fuel to be injected into the cylinder.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the second combustion parameter is a fuel injection timing, and when the control program causes the computer to determine the first combustion parameter and the second combustion parameter, the control program causes the computer to determine a final amount of fuel to be injected into the cylinder in the stratified combustion mode, based on the detected load, and determine the fuel injection timing based on the determined final amount of fuel to be injected into the cylinder.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
More preferably, after the fuel injection timing-determining module determines the fuel injection timing for a particular cycle of combustion, the second ignition timing-determining module determines the second ignition timing based on the determined fuel injection timing for the particular cycle of combustion.
According to this preferred embodiment of the control system, the second ignition timing for the stratified combustion mode can be optimized according to the fuel injection timing of the same combustion cycle.
More preferably, after the fuel injection timing for a particular cycle of combustion is determined at the step of determining the fuel injection timing, the second ignition timing for the particular cycle of combustion is determined based on the determined fuel injection timing at the step of determining the second ignition timing.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
More preferably, after the control program causes the computer to determine the fuel injection timing for a particular cycle of combustion, the control program causes the computer to determine the second ignition timing for the particular cycle of combustion based on the determined fuel injection timing.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the load-detecting module comprises an engine rotational speed-detecting module for detecting a rotational speed of the engine, an accelerator opening-detecting module for detecting an accelerator opening, and a demanded torque-determining module for determining a demanded torque based on the detected rotational speed of the engine and detected accelerator opening, as the load.
According to this preferred embodiment of the control system, the first ignition timing for the homogeneous combustion mode, and the first and second combustion parameters for the homogenous combustion mode and the stratified combustion mode can be properly determined based on the demanded torque determined based on the engine rotational speed and the accelerator opening.
Preferably, the step of detecting a load comprises the steps of detecting a rotational speed of the engine, detecting an accelerator opening, and determining a demanded torque based on the detected rotational speed of the engine and detected accelerator opening, as the load.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, when the control program causes the computer to detect the load, the control program causes the computer to detect a rotational speed of the engine, detect an accelerator opening, and determine a demanded torque based on the detected rotational speed of the engine and detected accelerator opening, as the load.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the control system.
Preferably, the engine includes a fuel injection valve for injecting the fuel into the cylinder, the cylinder having a top wall facing a combustion chamber, and the fuel injection valve is arranged in a central portion of the top wall such that the fuel injection valve injects the fuel downward therefrom.
According to this preferred embodiment, the advantageous effects provided by the control system and method and the engine control unit according to the fourth to sixth aspects of the invention and their preferred embodiments described above can be obtained in an optimized manner.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.